Revealing the Twohorns' of Taurus with GAIA

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Revealing the Two ‘Horns’ of Taurus with Gaia DR2

Graham D. Fleming,1 Jason M. Kirk,1 Derek Ward-Thompson,1 and Kate M. Pattle2, 3

1Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE, UK 2Institute for Astronomy and Department of Physics, National Tsing Hua University, No. 101, Section 2, Guangfu Road, Hsinchu 30013, Taiwan 3Centre for Astronomy, School of Physics, National University of Ireland Galway, University Road, Galway, Ireland

Submitted to ApJ

ABSTRACT We investigate the spatial properties of sources from the Gaia catalogue previously identified as being members of the Taurus star forming region and which appear in the Spitzer catalogue. We study an area of sky of 10◦×15◦, centred on Right Ascension (2000.0)=68.5◦ and Declination (2000.0)=27.0◦, this being an area surrounding the Taurus molecular cloud. We use data obtained from the Gaia DR2 release. By using an inversion of Gaia parallax measurements to obtain distance values and by defining limits to the proper motions of the Taurus moving group, we are able to show that there are substantial differences in depth within the Taurus complex. Our results suggest that the Taurus cloud has significant depth and that there are two main associations centred at ∼130±6 pc and ∼160±4 pc at 1σ. These two associations also have different proper motions, of 24.5±2.8 and 20.1±2.4 mas yr−1 respectively. We here label them the ‘Two Horns’ of Taurus.

Keywords: ISM: individual objects (Taurus molecular cloud) - stars: distances - parallaxes - proper motions

1. INTRODUCTION The Taurus molecular cloud (TMC) is one of the closest low-mass star-forming regions, lying at a commonly accepted distance of roughly 140 pc (Elias 1978). The region covers some 10 to 15 degrees in extent which equates to about 25 to 30 pc at this distance. This makes comprehensive studies of the entire stellar population of the region difficult and few comprehensive studies of the three-dimensional structure of the cloud complex have previously been conducted (e.g. Luhman 2018). Situated within the TMC are numerous filaments and smaller cloud structures (Hartmann 2002; Schmalzl et al. 2010; Kirk et al. 2013; Panopoulou et al. 2014; Marsh et al. 2016). Previous studies have shown that young stars are grouped in and around these smaller structures (Gomez et al. 1993; Kirk et al. 2013). Early distance measurements (McCuskey 1939) determined a distance of 142 pc to the Taurus star-forming region, whilst arXiv:1904.06980v3 [astro-ph.SR] 29 Jan 2020 later studies (Straizys & Meistas 1980; Meistas & Straizys 1981) of a number of Lynds dark clouds in the region (Lynds 1962) indicated that the TMC is more extended and exists between about 140 and 175 pc. +21 A study by Bertout et al.(1999) of three distinct regions of the complex placed the Lynds cloud L1495 at 125.6 −16 pc, +16 +42 the Auriga region at 140−13 pc, and the southern region at 168−28 pc. The investigation of early-type O and A stars located in the Taurus-Auriga molecular cloud (Mooley et al. 2013) within 1σ parallax error of 6.2< π <7.8 milli-arcsec (128 to 162 pc), identified a significant number of previously unidentified A5 or earlier stars within the region. Mooley et al.(2013) also noted in their study that even their new

Corresponding author: Graham D. Fleming gdfl[email protected] 2 distribution fell far short of the expected number of such stars if a standard log-normal IMF distribution is assumed for the region, adding to the discussion previously noted by Goodwin et al.(2004) and other researchers (e.g. Kraus et al. 2017). In their study, Bertout & Genova(2006) derived kinematic parallaxes of 67 members of the Taurus moving group +42 with typical errors of 20% and identified weak-line and classical T Tauri stars spread over distances between 106−24 +61 and 259−42 pc. Very Long Baseline Array (VLBA) parallax observations of the Taurus star-forming regions conducted by Torres et al.(2007, 2009) showed a difference in the distances to separate regions of the Taurus complex by studying a small sample of individual sources. They noted a distance of 161.2±0.9 pc for the star HP Tau/G2 and 146±0.6 pc for T Tau (from Loinard et al.(2007)) in the eastern part of the complex, and 130 pc to the central area of the star-forming complex, by observing the T Tau-type stars Hubble 4 (V* V1023 Tau) at 132±0.5 pc and HDE 283572 at 128.5±0.6 pc. A multi-wavelength photometric study of the Taurus region Gudel et al.(2007) using Spitzer and XMM- Newton data produced large-scale maps detailing the stellar and substellar distribution of the region, and in a similar survey of the TMC conducted by Rebull et al.(2010), pre-main sequence members of the Taurus molecular clouds were identified using the Spitzer Space Telescope Taurus project (SSTtau) catalogue (http://cds.u-strasbg.fr/cgi- bin/Dic-Simbad?SSTtau) and Two-Micron All-Sky Survey (2MASS) data (http://vizier.u-strasbg.fr/cgi-bin/VizieR?- source=B/2mass). In other, more recent research, planetary-mass brown dwarfs in the Taurus and Perseus star-forming regions have been investigated using photometric and proper motion data from a number of space and ground-based platforms including Spitzer and Gaia DR1 (Esplin & Luhman 2017). Galli et al.(2018) presents trigonometric parallax and proper motion observations of Young Stellar Objects (YSOs) in the Taurus region as part of the Gould Belt Distances Survey using the VLBA. Their data suggest a significant difference between the closest and farthest stars in their sample of about 36 pc with the closest lying at 126.6±1.7 and the most distant at 162.7±0.8 pc. Within this range they noted that the central portion of the L1495 dark cloud is at 129.5±0.3 pc, whilst the supposedly associated B216 structure lies at 158.1±1.2 pc. The more recent comparison of Gaia DR2 and VLBI astrometry results (Galli et al. 2019) revise these distances but again confirm the existance of significant depth effects within the TMC. Contemporary studies of the TMC using Gaia DR2 data conducted by (Luhman 2018; Esplin & Luhman 2019), present comprehensive studies of the stellar membership of the Taurus region. In both studies extensive reference is made to earlier works with regard to the stellar membership of specific cloud complexes within the TMC and the kinematics of their members. No evidence for an older population of stars previously identified by Kraus et al.(2017) and Zhang et al.(2018) is found, however the existence of a possible moving group of stars at a distance of 116 to 127 pc with ages of ∼40 Myr first identified in the Gaia DR1 data by Oh et al.(2017) is suggested. Previous studies such as those listed above have identified significant distance dispersion among the stellar members of various regions within the TMC star-forming complex, and have further suggested considerable depth effects within the cloud. In contrast to more recent studies, we revisit the coherent catalogue of sources identified by Rebull et al. (2010) in the Spitzer SSTtau catalogue and use the newly available data from Gaia data release 2 to model the characteristics and detailed internal distribution of sources within the region as a whole (Brown et al. 2018; Luhman 2018). Where our studies overlap, we note that our findings are consistent with those of Luhman(2018) and Galli et al.(2019) and consider them complementary to the results of these studies. Section2 provides a brief overview of the Gaia mission and some of the relevant issues concerning DR2. The acquisition of data and its subsequent analysis are discussed in §3 with particular attention being paid to the statistical treatment of the data. Section4 presents a discussion of our data which is briefly summarised in §5. A compendium of the sources discussed in this study are presented in the Appendix.

2. GAIA The European Space Agency Gaia astrometric space observatory (Lindegren & Perryman 1996) was launched in December 2013. The spacecraft is designed to measure the parallax, positions and proper motions of stars, with the ambitious goal of producing a three-dimensional map of most of our Galaxy. Gaia is not designed to measure distances directly, but they can be inferred through the determination of stellar parallax. The Gaia Archive1 is a relational database which can be accessed through an interactive user interface and interrogated using conditional queries.

1 http://gea.esac.esa.int/archive/ 3

The second Gaia data release (DR2) occurred in April 2018 with a five-parameter astrometric solution for more than 1.33×109 sources (Brown et al. 2018). DR2 parallax uncertainties are in the range of up to 0.04 milli-arcseconds (mas) for sources with a broad-band, white-light magnitude (G) <15 and in the order of 0.7 mas at G=20. Coupled with proper motion measurements from DR2, a detailed investigation of the internal kinematics of the Taurus star-forming region can be made. Due to the relative proximity of the Taurus star-forming region, where the parallaxes are positive and relative uncertainties are small, a Bayesian prior is not employed in this study (Bailer-Jones 2015; Bailer-Jones et al. 2018; Luri et al. 2018), and a straightforward inversion of parallax is used to infer distance. This does not affect any of the conclusions in this paper. Since it is known that there are unquantifiable (but probably small) parallax errors due to a poorly determined zero-point offset in extinction (Lindegren et al. 2018), it is not possible to correct individual Gaia parallax values completely. It should also be remembered that Gaia is, in essence, an optical telescope and, as such, will have difficulty in accurately measuring parallaxes in areas of high optical extinction due to dust. Hence, for the purposes of this study, mean parameter values are used. Independent comparisons of Gaia and VLBA studies of YSOs in the Ophiuchus, Serpens and Aquila regions (Ortiz-Leónet al. 2018) obtained consistent parallax values across all systems, supporting our use of uncorrected Gaia parallax values at this distance.

3. DATA 3.1. Selection and discussion Sources towards the Taurus region were selected using a 15◦×10◦ box centred on RA (2000.0)=68.5◦ and Dec (2000.0)=+27.0◦. This effectively defines an area on the sky of roughly 126 pc2 at the approximate distance of the Taurus cloud. Parallax values were set between 5.0 and 10.0 mas, setting a box covering a distance range from 100 to 200 pc. Quality limits were set to only include data with at least 5 independent astrometric measurements. No other quality flags were defined, so as to maximise the number of sources returned, thereby enabling an objective selection of sources within the study area. After performing distance calculations on the mean parallax values of the sources returned, the results were plotted on a histogram in 1 pc bins. The subsequent distribution showed no evidence of the expected peak in population at around 140 pc. We hypothesised that this was due to the Taurus sources being totally swamped by foreground and background objects. To remove possible contamination of our sample by foreground and background field stars, we cross-referenced our findings with the Spitzer SSTtau catalogue (Rebull et al. 2010) and obtained 168 objects in our search area with known Gaia parallaxes and proper motions.

6 all sources Brown Dwarf 8 Galli et al. (2018)

14 G [mag]

20 KPNO-Tau4 5 6 7 8 9 10 parallax [mas]

Figure 1. Parallaxes, with errors, of the 168 Gaia DR2 sources identiﬁed in the Spitzer SSTtau catalogue of Taurus members, plotted against G-Band mean magnitude. Sources identiﬁed in the SIMBAD Astronomical Database as brown dwarfs are shown in magenta whilst those cross-matched to Galli et al.(2018) are in cyan.

Within this subset the largest parallax error is 1.214 mas for object Gaia DR2 151265002954775936 (KPNO-Tau4), which is a classiﬁed L0 brown dwarf (see Figure1). It should be noted, that brown dwarfs within the sample typically have higher parallax errors, suggesting constraints on the detection of such low luminosity objects. Parallax errors on the remaining sources are signiﬁcantly lower. Parallax errors in relation to Gaia DR2 G-band magnitude 4

(phot g mean mag) for the sources identiﬁed in the Spitzer catalogue are presented in Figure1 which clearly shows a double peaked scattering in the parallax (and hence, distance) distribution of the sources. Figure1 also provides a comparison to those of our sources which are present in the Galli et al.(2018) study and it can be seen that these sources are amongst the brightest of those in our study. The properties of the 168 Gaia sources are listed in Table3 in AppendixA. Taking inverse parallax values and determining the distances of our sample of 168 sources, we binned the values at 3 pc intervals and produced a distance distribution. The resulting distribution is plotted in Figure2. The same double-peaked distribution seen in Figure1 is visible.

25 110-150 pc 150-180 pc d = 147.9 pc Unassigned 20

10 Histogram Frequency

0 100 120 140 160 180 200 Distance [pc]

Figure 2. Distance distribution of 168 Gaia DR2 sources identiﬁed in the Spitzer SSTtau catalogue of Taurus members. Sources are grouped in 3-pc bins. Two distinct groupings are seen. A double-Gaussian curve is ﬁtted identifying a minimum value at 147.9 pc (see text for details).

A double-Gaussian curve (shown in black) is ﬁtted (Figure2) indicating a minimum in the bi-modal distribution at 147.9 pc, hereafter taken to be ∼150 pc.

3.2. Validation of Gaia DR2 distance data We have compared the Gaia DR2 distance data with previous VLBA determinations (Torres et al. 2009; Galli et al. 2018) to draw comparisons between the two sets of observations and find nine sources common to both studies. These sources are amongst the brightest of our sources and are identified in Figure1, showing their Gaia G-Band mean magnitudes. Figure3 plots the two sets of distances of these common sources. It can be seen that that the Gaia DR2 derived values are roughly consistent with previous measurements. There are three sources which show large errors, Gaia DR2 147778490237623808 (V807 Tau B), Gaia DR2 148116246425275520 (V999 Tau) and Gaia DR2 163233981593016064 (V1096 Tau). SIMBAD identifies V999 Tau and V1096 Tau as being M0.6 class T-Tauri stars whilst V807 Tau B is listed as a K7 T-Tauri star. Gaia DR2 G-band extinction data for V1096 Tau is recorded as being 2.97 mag but is incomplete for the other two sources, it is therefore not possible to make a definitive judgement concerning the large errors displayed by these objects. However, agreement for the other sources is clearly seen.

3.3. Statistical analysis of distance distribution To analyse the distribution of our sources we used Hartigans’ dip test for uni-modality (Hartigan et al. 1985; Maurus & Plant 2016). This is recognised as being a robust statistical measure of the modality of a continuous distribution where the ‘dip’ measures the departure of a distribution from uni-modality. The Hartigan Dip Statistic (HDS), corresponding to the probability ‘p-value’, is determined by repeatedly sampling the maximum difference between the observed distribution of data and that of a uniform distribution that is chosen to minimize this maximum difference. P-values <0.05 are an indication of significant bi-modality and values greater than 0.05 but less than 0.10 suggest bi-modality with marginal significance. We obtained a p-value of 0.025. This value suggests that we reject the null hypothesis of uni-modality. We therefore identify our distribution as bi-modal with a boundary between the two groups at ∼150 pc. 5

170 Linear Relationship Common Sources

160

150

140 V807 TauB

130 V1096 Tau

Distance (pc) - GAIA DR2 120

110 V999 Tau

110 120 130 140 150 160 170 Distance (pc) - Galli et al. (2018) [Table 8]

Figure 3. Comparison of Gaia DR2 and VLBI (Galli et al. 2018) distance data for the nine common sources.

Having statistically identiﬁed that our distance distribution represents two independent populations we split them into ‘near’ and ‘far’ groups using the ∼150 pc boundary to give groups lying between 110 to 150 pc and 150 to 180 pc respectively. Figure2 identiﬁes our two groups, colour coded red and blue for the ‘near’ and ‘far’ groups respectively. The three sources coded white lie outside the two main populations and are not discussed hereafter. We here identify our two main groups as the ‘Two Horns’ of Taurus. Our analysis is consistent with other recent Gaia studies of Taurus (Luhman 2018; Esplin & Luhman 2019).

3.4. Proper Motion studies A number of proper motion studies have previously been undertaken of this region, notably those conducted by Jones & Herbig(1979); Walter et al.(1987); Hartmann et al.(1991); Gomez et al.(1992); Frink et al.(1997); Ducourant et al.(2005); Bertout & Genova(2006) and more recently (Dzib et al. 2015) and Galli et al.(2018). In general, these are all studies of pre-main sequence stars, seeking to identify the proper motions, µ, of members of the Taurus group. Table1 lists the mean, upper and lower proper motion values from these studies. We have used these to constrain the upper and lower limits of proper motion for this study of the TMC. All 168 identified sources (see AppendixA, Table3) have Gaia DR2 proper motions, and of these, 165 lie within the ‘near’ and ‘far’ populations mentioned above – the remaining 3 are shown in white in Figure2. Based on the literature values given in Table1, for the purposes of this study, upper and lower limits of proper motion for the Taurus moving group are taken as being 40 mas yr−1 and 12 mas yr−1 respectively. Within these limits there are 161 sources. The four sources which lie outside of our limits have µ values of 5.41, 9.05, 43.38 and 45.40 mas yr−1 which are consistent with the upper and lower ranges discussed in the literature, but in AppendixA, Table3 we discounted these µ values since they are derived using extreme values of either RA or Dec. Discounting these four sources, our minimum, mean and maximum values of proper motion are given in Table1. Using a k-Means clustering algorithm we analysed this group to investigate whether there is a proper motion ’split’ associated with the distance distribution and to determine the centroids of the groups if such an association exists. We find that such an association does exist and that the mean proper motions of the two groups are different. There are 111 members in the ‘near’ group and 50 in the ‘far’ group – the remaining 4 sources are rejected as lying outside of this 12–40 mas yr−1 proper motion cut. The mean proper motion of the ‘near’ population is 24.5±2.8 mas yr−1, and that of the ‘far’ population is 20.1±2.4 mas yr−1. The proper motions of 156 of the 161 stars are shown in Figure4 (the colour coding of the two groups is the same as in Figure2). Figure4 has been ‘zoomed-in’ to show the bulk of the sources more clearly – so there are five sources lying within our proper motion limits of 12–40 mas yr−1, but which are outside the plotted boundaries of Figure4. Of these five, two belong to the ‘near’ population (Gaia DR2 146675954953119104 and Gaia DR2 147546080967742720), and three lie in the ‘far’ population (Gaia DR2 148116276529733120, Gaia DR2 147248216395196672 and Gaia DR2 145213192171159552). One of these sources, Gaia DR2 145213192171159552 (CoKu HP Tau G2) has been previously studied (Torres et al. 2009) using the VBLA, which determined a parallax of 6.2±0.3 mas. Our Gaia DR2 value is 6.02±0.04 mas and is fully consistent. 6

Table 1. Taurus proper motion values in the literature.

Reference µmin µmean µmax (mas yr−1) (mas yr−1) (mas yr−1) Jones & Herbig(1979) ··· 22.80 ··· Frink et al.(1997) ··· 21.24a ··· Bertout & Genova(2006) 9 .37 22.38 41.22 Slesnick et al.(2006) b 13.89 ··· 43.05 Torres et al.(2009) c · · · ∼ 20.0 ··· Galli et al.(2018) d 15.0 ∼ 22.0 39.0 Mean literature valuese 12.75 22.14 41.09 This study 11.94 23.02 30.60 a Value given for the central part of the Taurus-Auriga cloud system. b Values derived from their ﬁgure 9 (lower histogram). c cited in Dzib et al.(2015). d Maximum and minimum values obtained from their ﬁgure 2. e Ignoring imprecise values from Torres et al.(2009) and Galli et al. (2018).

10.0 110-150 pc 150-180 pc 12.5 centroids

1 15.0 20.1±2.4 mas yr

] 17.5 1 r y

a 20.0 m [

22.5 24.5±2.8 mas yr 1 25.0

27.5

30.0 0 2 4 6 8 10 12 14 1 * [mas yr ]

Figure 4. Proper motions for the ‘near’ and ‘far’ populations of 156 of the stars shown in Figure2 with proper motion limits of 12 mas yr−1 to 40 mas yr−1. Colour coding is the same as in Figure2. Two populations of proper motion groupings can be seen which are consistent with the two distance groupings seen in Figure2. There are 2 red and 3 blue outlying sources beyond the area shown on this plot (see text for details).

For comparison, 7 sources from the study of Galli et al.(2018) lie within our ‘near’ population and 2 lie in the ‘far’ group. These numbers are statistically low, nevertheless they provide mean proper motions of 24.90±4.88 and 19.66±0.50 mas yr−1 for the ‘near’ and ‘far’ populations respectively, which are fully consistent with the values found here.

4. DISCUSSION It has been seen (Figure2) that there are two signiﬁcant peaks in the distance distribution, centred at approximately 130 and 160 pc. Separating these peaks into ‘near’ and ‘far’ populations, as indicated by the red and blue colouring in Figure2, results in mean (and error on the mean) distances for each component of 130.6 ±0.7 and 160.2±0.9 pc respectively. For these groups the standard deviation on the distance is ∼6 & ∼4 pc respectively versus a mean error 7 on each measurement of ∼4-5 pc. It is probable that the standard deviations for the distances are broadened by these measurement errors. Table2 shows the parameters of each group. These distributions are roughly consistent with the ﬁndings of previous studies mentioned in §1, but far more double-peaked than was previously realised.

Table 2. Properties of the near (red) and far (blue) populations shown in Figures2 and4. a

Number Mean Standard µα cos δ µδ |µT otal| Standard Angle Standard of Sources Distance Deviation Deviation θ Deviation

[pc] [1σ] [mas yr−1] [mas yr−1] [mas yr−1] [1σ] [degrees] [1σ] Near 111 130.6 ± 0.7 6.7 7.5 −23.1 24.5 2.8 162 6 Far 50 160.2 ± 0.9 4.5 8.9 −17.3 20.1 2.4 154 17 a Statistics are calculated after distance and proper motion cuts have been made.

For the purposes of simplicity, we have identified our groups as lying at 110–150 pc and 150–180 pc respectively. From Figure4 it can be seen that these two populations have markedly different proper motion characteristics. The populations fall within two separate and distinct proper motion groups, related to their distance. The mean proper motions of the two groups are listed in Table1, and are 24.5 ±2.8 and 20.1±2.4 mas yr−1 for the ‘near’ and ‘far’ populations respectively. The mean angles, θ, of the proper motions of the two populations are also listed in Table2, along with their standard deviations. These are 162±6◦ and 154±17◦ for the ‘near’ and ‘far’ populations respectively, where all angles are measured east of north. To confirm that our two groups are contained within the same distribution we examined our proper motion groups using a general-purpose non-parametric two-sample Kolmogorov-Smirnov (KS) test (Kolmogorov 1933). This two- sample test does not assume that data are taken from Gaussian distributions and is sensitive to differences in both location and shape of the two samples. This test is recognised by Peacock(1983) as being a powerful tool in the analysis of astronomical data. However, we recognise that caution needs to be taken when using this test in astronomical applications (e.g. Feigelson & Babu 2013; Stephens 1974). The p-value provided by this test can be interpreted in the same way as p-values for other such tests. If the p-value is small, the null hypothesis that the two samples were drawn from the same distribution can be rejected and it can be assumed that the two groups were sampled from populations with different distributions. We obtain a p-value of 4×10−17 which supports our earlier identification of a non-unimodal distribution (see §3.3) and rejects the possibility that the two groups come from the same population.

4.1. Group and structure correlations Using the data presented in Figures2 and4 it is now possible to obtain a picture of the distribution of objects within our sample region. Figure5 presents this distribution superposed on a visual extinction map of the region calculated from the 2MASS survey (Schneider et al. 2011). Obvious structures within the distance distribution of sources are identifiable within the cloud complex. For example, Gaia DR2 164422961683000320 (V1070 Tau), which lies within the south-eastern region of Barnard’s Cloud B10 (part of the extended Lynds L1495 filament), is found to +21 lie at 126.4±1.6 pc, which is consistent with the value of 126−16 pc found earlier by Bertout et al.(1999). The region around B10 can thus be seen to be part of the ‘near’ population, and the 31 sources associated with the ‘near’ group within B10 are found to have a mean distance of 131.9±3.2 pc, with a standard deviation of 5.0 pc. Stretching away to the south-east from B10 lies the L1495 filament and its associated clouds B211 and B213. There are a number of sources from both populations which lie directly within, or close to this structure. It is apparent that, if these sources are genuinely associated with the filament, then there appears to be a double distance gradient along this structure. One interpretation of this apparent double gradient is that the cluster of ‘far’ population sources roughly aligned with B213, are actually background to it. For this to be the case, there would need to be gaps in the foreground cloud that allowed the background region to be seen. This explanation would be consistent with the findings of Hacar et al.(2013), if one interprets their line-of-sight velocity with distance. This hypothesis is pursued 8

N 110-150 pc B10 150-180 pc W 28° V1070 Tau B211 Heiles Cloud 2 B213 L1495

TMC-1 26°

B18 Declination (J2000) 24°

L1536 22° 4h48m 36m 24m 12m Right Ascension (J2000)

Figure 5. Spatial distribution of Gaia DR2 sources identified in the Spitzer SSTtau catalogue, using appropriate selection criteria (see text for details). Sources have been identified according to distance and overlaid on a visual extinction map calculated from the 2MASS survey (Schneider et al. 2011). The colour coding is the same as in Figures2 and4. It can be seen that both B10 and B18 are dominated by sources in the ‘near’ group. L1536 is predominantly composed of sources from the ‘far’ population. See text for further discussion. further in §4.3.1 below. Cloud B18 appears to be populated with a discrete population belonging to the ‘near’ group. Analysis of the data for this group shows that they are lying at a mean distance of 127.4±3.8 pc, with a standard deviation of 7.9 pc. The VLBA derived parallax to the star HP Tau/G2 in L1536 provides a distance of 161.2±0.9 pc (Torres et al. 2009). HP Tau/G2 also appears in the Galli et al.(2018) study with a derived mean distance of 162.7 ±0.8 pc, which is within 3σ of the Gaia value of 165.9±1.3 pc. This star is embedded within the reflection nebula GN 04.32.8, which appears as a crescent-shaped feature in the Herschel column density map of L1536 (Kirk et al. 2013). HP Tau/G2 (Gaia DR2 145213192171159552) lies within the area of L1536 (Figure5). There are 20 ‘far’ group sources identified in this area with a mean distance of 160.3±3.7 pc, and a standard deviation of 6.8 pc. The clear interaction of HP Tau/G2 with L1536 strongly implies that L1536 is at a comparable distance (Kirk et al. 2013). This is also supported by +42 the earlier study of Bertout et al.(1999), which placed the southern region of the Taurus cloud at 168 −28 pc. There are seen to be two members of the near population situated within, or close to the L1536 region. These are Gaia DR2 145238687096970496 and Gaia DR2 145157937416226176 which have distance determinations of 130.0±2.3 and 140.3±4.2 pc respectively. When considering their maximum distances, they do not fall within the lower boundary of the ‘far’ group and we thus consider their proximity to L1536 as a fortuitous alignment and discount them as being members of L1536. The association of our groups with the discrete structures within the Taurus cloud is graphically highlighted by Figure5. With the addition of the Gaia DR2 derived distance data we are able to develop a three-dimensional picture of this region. So, we studied the 3-D spatial distribution of our sources in Galactic X, Y, and Z as well as celestial ICRS Right Ascension and Declination. Figure6 presents our 165 sources in the Galactic reference frame ordered by Right Ascension. Of interest here are the lower panels which plot Galactic Z-Y and X-Y with the colour plots ordered by Right Ascension. The ‘near’ and ‘far’ group affiliations previously noted in the ICRS reference frame are clearly seen in Cartesian space with the spatial alignments, suggesting that the TMC is consistent with a structure similar to that of an inclined sheet facing away from us. 9

30 72

29 71

80 70 28 69 27 68 70 26 67

Declination 25 66 Right Ascension

z [parsec] 60 24 65

23 64

22 63 50 72 70 68 66 64 Right Ascension

160

150

140

130

y [parsec] 120

110

100

40 50 60 70 50 60 70 80 x [parsec] z [parsec]

Figure 6. Distribution of 165 sources in the Galactic reference frame. The lower panels suggest that the stellar distribution resembles a ’sheet like’ structure (see text).

4.2. TMC-1 and the Taurus Molecular ‘Ring’ (TMR) Here, we consider the TMC-1 region in more detail. The area commonly known as the ‘Bull’s Tail’ (Nutter et al. 2008) lies within a region previously referred to as the Taurus Molecular ‘Ring’ (TMR), which is associated with the low mass star-forming Heiles Cloud 2 and has been the subject of many previous investigations (e.g. Hartigan & Kenyon 2003; T´othet al. 2004; Nutter et al. 2008; Malinen et al. 2012). Previous studies of this feature provided a generic distance of ∼140 pc in common with the region as a whole. However, Nutter et al.(2008) showed that this putative ‘ring’ is not a coherent structure, but rather a chance alignment of discrete sources with diﬀerent line-of-sight velocities. 10

Objects Gaia DR2 148401565437820928 and Gaia DR2 148400229703257856 lie in the central region of the ‘Bull’s Tail’ and have Gaia DR2 derived distances of 136.3±8.2 and 136.9±2.1 pc respectively, which are in general agreement with previous studies. From Figure5 it can be seen that there is a member of the ‘far’ group to the south of the ‘Bull’s Tail’ (Gaia DR2 148374391180009600). The association of members of both the ‘near’ and ‘far’ populations with this feature supports the previous suggestion of Nutter et al.(2008) that the TMR is not a coherent feature but is rather composed of disparate sources at diﬀerent distances spread throughout the depth of the complex.

N 147.5 W 26°30' 145.0

142.5 00' 140.0

DR2 148374391180009600 137.5 25°30' Distance (pc) Declination (J2000) 135.0

00' 132.5

4h40m 36m 32m 28m Right Ascension (J2000)

Figure 7. The region around TMC-1 with sources colour coded by distance. The putative ‘ring’ is situated to the east of the ﬁgure which clearly shows that the feature has signiﬁcant depth.

Further, the region around the putative ‘ring’ is seen to the east of 4h 36m in Figure7. It can clearly be seen that objects in this area have a spread in distance of some 10 to 15 pc. We are thus able to support the hypothesis of Nutter et al.(2008) that the so-called ‘ring’ is not a coherent structure.

4.3. Velocity distributions within the TMC Here we look at the ‘true’ proper motions of our two populations by comparing literature values with our own ﬁndings.

4.3.1. Comparison between distance and line-of-sight velocity We compare our interpretation of the three-dimensional nature of the TMC with existing line-of-sight velocity measurements of the region. It is well-established that the TMC has a complex velocity structure (e.g. Clark et al. 1977). In the context of the Gaia distance observations, it is a useful exercise to attempt to associate the stars in our ‘near’ and ‘far’ groups with the major line-of-sight velocity components of the cloud. The 12CO emission associated with the TMC has systemic line-of-sight velocities ranging from ∼ 0−12 km s−1, with the large majority of the emission having velocities in the range 4 − 8 km s−1 (Narayanan et al. 2008). The TMC has an overall east-to-west velocity gradient, with the eastern parts of the cloud preferentially having a lower systemic velocity than those in the west (e.g. Goldsmith et al. 2008). However, there is a great deal of variation within this broad east-to-west trend. Particularly, the L1495 filament is known to have two distinct velocity components, separated by ∼ 1.5 km s−1 (e.g. Heiles & Katz 1976; Clark et al. 1977). Hacar et al.(2013) used C 18O observations to further separate these two components into multiple sub-filaments, with one set of sub-filaments having velocities ∼ 5 − 6 km s−1, and the other having velocities ∼ 7 km s−1. The well-defined plane-of-sky morphology of the L1495 filament is at odds with its apparent lack of velocity coherence, leading to suggestions that the ‘filament’ may in fact be an edge-on sheet (e.g. Palmeirim et al. 2013). However, Li & Goldsmith(2012) compared volume densities derived from dense gas tracers with 2MASS-derived column densities, and found that the high-density portion of the L1495 ‘filament’ has a plane-of-sky depth of only ∼ 0.12 pc, suggesting that it is indeed an approximately cylindrical structure. The stars associated with the TMC included in the Gaia DR2 catalogue are located at intermediate visual extinction, and so are not associated with the densest star-forming gas. We thus compare the distribution of the stars in our two distance groups to the velocities measured in 12CO observations of the TMC (Narayanan et al. 2008; Goldsmith et al. 2 3 −3 2008). These observations trace moderately dense gas (n(H2) ∼ 10 − 10 cm ) which is definitively associated with the TMC, but which is not gravitationally unstable and actively forming stars (e.g. di Francesco et al. 2007). 11

12CO velocity channel maps presented by Narayanan et al.(2008) show that the B10 and B18 regions have systemic velocities ∼ 7 km s−1, while the L1536 region has a systemic velocity ∼ 5 km s−1. The L1495 filament shows a double- peaked velocity structure, as discussed above. The TMC-1 region also has multiple velocities, with some suggestion that the eastern side of TMC-1 is at a lower systemic velocity (∼ 5 − 6 km s−1) than the western side (at ∼ 7 km s−1). We find a correspondence between these behaviours and the spatial distribution of the stars in our ‘near’ and ‘far’ groups (see Figure5). B10 and B18 are both dominated by ‘near’ stars, and have a systemic velocity of ∼ 7 km s−1, while L1536, containing ‘far’ stars, has a systemic velocity ∼ 5 km s−1. The L1495 filament, with its two velocity components, contains stars from both groups, as does TMC-1. However, in TMC-1 the ‘far’ stars are preferentially located in the east, while the ‘near’ stars are preferentially located in the west, corresponding to a velocity gradient from ∼ 5 − 7 km s−1 across the region. There is thus a qualitative tendency for ‘near’ stars to be associated with ∼ 5 km s−1 sight-lines, and for ‘far’ stars to be associated with ∼ 7 km s−1 sight-lines. Our results thus tentatively suggest that the two main velocity components of the gas in the TMC are located at different line-of-sight distances, with the ∼ 5 km s−1 gas being located in front of the ∼ 7 km s−1 gas. The ‘gaps’ in the L1495 filament hypothesised in Section 4.1 are also seen in the velocity data.

4.3.2. Velocity directions The Right Ascension and Declination proper motions of our sample sources are detailed in TableA. When these values are translated into vectors, as shown in Figure8 (left), it can be seen that there is a small diﬀerence in the vectors between the two populations. The mean values of proper motion for each population and their standard deviations are given in Table2. The arrows indicate the proper motions of the stars. However, for a proper analysis of the relative proper motions the inﬂuence on these motions caused by the solar motion and Galactic rotation need to be taken into account. Literature studies suggest that this transform is particularly sensitive to the Oort constants (Oort et al. 1927; Olling & Dehnen 2003), in particular the ’V’ component of the solar motion relative to the Local Standard of Rest, which is unknown by up to a factor 2.

N N 110-150 pc 110-150 pc 150-180 pc 150-180 pc W W 28° 28°

26° 26° Declination (J2000) Declination (J2000) 24° 24° HD 30067

22° 22° 4h48m 36m 24m 12m 4h48m 36m 24m 12m Right Ascension (J2000) Right Ascension (J2000)

Figure 8. Group distributions within the TMC and related velocity vectors. Left: Proper motions of the ‘near’ and ‘far’ groups identiﬁed in Figure2 (see text). Individual star proper motions displayed as vectors, showing direction and relative magnitude of velocity. Right: Proper motions after the removal of Solar and Galactic motion components towards Taurus.

We use the value of Oort constants from Li & Goldsmith(2012) and the Solar velocities from Schönrich et al.(2010) using the convention for solar velocities in the Galactic coordinate system as: U being the component toward the Galactic Center; V the component along the line of Galactic rotation; and W being the component out of the Plane, towards the Galactic North Pole. Since it is also necessary to use a rotation matrix to transform between celestial ICRS (RA,Dec) and Galactic (l,b) coordinates we use the technique presented by Li et al.(2019). We also consider the treatment of barycentric stellar motion in astrometric and radial velocity data. The rigorous treatment of the epoch propagation, including the effects of light-travel time, was developed by Butkevich & Lindegren(2014). However, for the propagation of the prior information to the Gaia reference epoch, it is sufficient to use the simplified treatment, which was employed in the reduction procedures used to construct the Hipparcos and Tycho catalogues, since the light-time effects are negligible 12 at milliarcsecond accuracy. The resultant velocity vectors of the two groups, taking Galactic rotation into account is presented in Figure8 (right). The treatments of proper motion velocity vectors presented in Figure8 clearly show a marked difference in the proper motions of the two populations, in particular those of the members of L1495 and L1536. In an X-Ray survey Briceno et al.(1997) suggested that a population of stars discovered during the ROSAT mission (Trümper 1985), located to the south of the Taurus clouds, might be an older population and have a different origin from the rest of the cloud, as well as being located at a different distance to the then commonly accepted distance of 140 pc. Our initial findings tend to support these ideas and further suggest that there may be a dynamic link between L1536 and the B213 region within L1495. Considering Figure8 (right), one star stands out from the rest. Within the ‘far’ population, HD 30067 (Gaia DR2 147248216395196672) is found to have a markedly different velocity profile to the rest of its group. This star is noted Rebull et al.(2010) as being an A4V Class III YSO and is recorded in SIMBAD as being an A2/4 class star located at 163.5±1.4 pc with a proper motion of µ = 16.1 mas yr−1. Gaia DR2 indicates a G-Band magnitude of 8.9 mag and an extinction of 4.5 mag for this source. We suggest that, although this star meets the distance and proper motion criteria described earlier, HD 30067 is actually a runaway field star and not associated with the Taurus group.

5. SUMMARY This study has shown, through the use of trigonometric parallaxes from Gaia DR2, that there are significant differences in the distances to different structures within the Taurus molecular cloud complex. We have shown that there are two main associations located at 130.6±0.7 and 160.2±0.9 pc. The two groups have different proper motions of 24.5±2.8 and 20.1±2.4 mas yr−1 respectively, and they appear to be moving in somewhat different directions. They also appear to have slightly different line-of-sight velocities. We call these two populations the ‘Two Horns’ of Taurus. With this new data we have also been able to confirm that the TMR is not a coherent feature but has an extended depth of approximately 15 parsecs. We also tentatively suggest that the structure of the TMC, in general, resembles that of an inclined sheet facing away from the observer.

We thank the anonymous referees for their constructive comments. Use has been made of data from the European Space Agency (ESA) mission GAIA (https://www.cosmos.esa.int/gaia), processed by the GAIA Data Processing and Analysis Consortium (DPAC) (https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the GAIA Multilateral Agreement. This work has used the NASA Astrophysics Data System (ADS) Bibliographic Services (http://ads.harvard.edu/) as well as the VizieR catalogue access tool (http://vizier.u-strasbg.fr/viz-bin/VizieR) and SIMBAD astronomical database (http://simbad.u-strasbg.fr/simbad/), operated at CDS, Strasbourg, France. Data products have also been used from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has made use of Astropy, a community-developed core Python (https://www.python.org/) module for Astronomy (Robitaille et al. 2013; Price-Whelan et al. 2018). This work has also made extensive use of Matplotlib (Hunter 2007), SciPy (Van der Walt et al. 2014) and NumPy (Van Der Walt et al. 2011). This work would not have been possible without the countless hours put in by members of the open-source community around the world. DWT was supported by the UK Science and Technology Facilities Council under grant number ST/R000786/1. KP acknowledges support from the Ministry of Science and Technology (Taiwan) under Grant No. 106-2119-M-007-021- MY3.

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APPENDIX A. COMPENDIUM OF SOURCES In this Appendix we list all of the parameters of the 168 sources in our sample, before we applied the ﬁnal distance and proper motion cuts. The reader may therefore judge the validity of cutting from 168 to 161 sources.

Table 3. Properties of Gaia DR2 Taurus sources.

Gaia DR2 ID SSTtau ID R.A. Dec. Parallax Distance PMRA PMDec µ

[deg] [deg] [mas] [pc] [mas yr−1] [mas yr−1] [mas yr−1]

147869573608324992 043051.7 + 24414 67.7156 24.6965 9.51 105.12 11.52 −24.50 27.10 151870352825256576 043545.2 + 273713 68.9387 27.6202 8.83 113.19 14.20 −25.79 29.44 147778490237623808 043306.6 + 240954 68.2777 24.1652 8.83 113.20 9.56 −20.23 22.37 149685627517927296 042359.7 + 251452 65.9988 25.2479 8.75 114.33 0.99 −19.70 19.72 147546080967742720 043621.5 + 235116 69.0896 23.8545 8.66 115.46 −1.54 −19.48 19.54 151296579553731456 043007.2 + 260820 67.5302 26.1390 8.62 116.06 2.67 −21.927 22.09 164513602672978304 041840.6 + 281915 64.6692 28.3209 8.52 117.44 6.62 −29.87 30.60 164513022853468160 041807.9 + 282603 64.5333 28.4342 8.48 117.95 8.43 −24.73 26.13 149409920679460096 042630.5 + 244355 66.6273 24.7321 8.41 118.91 2.74 −22.02 22.19 164502062096975744 041901.1 + 281942 64.7546 28.3282 8.38 119.37 8.71 −25.34 26.79 164598303725243776 041935.4 + 282721 64.8978 28.4560 8.36 119.64 11.93 −25.97 28.58 164550882989640192 042203.1 + 282538 65.5132 28.4274 8.31 120.27 10.27 −25.86 27.83 146874275068113664 044000.6 + 235821 70.0028 23.9724 8.30 120.49 8.62 −20.74 22.46 151262700852297728 042704.6 + 260616 66.7696 26.1044 8.25 121.18 6.16 −19.30 20.26 164546038266077824 042025.8 + 281923 65.1077 28.3232 8.19 122.13 10.66 −24.22 26.46 151102790629500288 043057.1 + 255639 67.7384 25.9442 8.14 122.82 5.42 −23.02 23.65 148116246465275520 044205.4 + 252256 70.5229 25.3822 8.14 122.88 5.49 −18.99 19.77 164507353496637952 041831.1 + 281629 64.6297 28.2747 8.12 123.08 8.82 −25.64 27.12 165563674934601856 041357.3 + 291819 63.4891 29.3053 8.10 123.47 9.95 −22.89 24.96 146764465639042176 043906.3 + 233417 69.7766 23.5716 8.06 124.14 8.18 −21.82 23.30 147799209159857280 043217.8 + 242214 68.0745 24.3707 8.05 124.17 6.26 −22.20 23.06 164519276325850752 041817.1 + 282841 64.5713 28.4782 8.04 124.37 5.79 −25.03 25.69 146675954953119104 043815.6 + 230227 69.5651 23.0409 7.98 125.24 −1.07 −17.19 17.22 164513400810646912 041842.5 + 281849 64.6771 28.3138 7.97 125.50 12.13 −24.15 27.02 164495323291866624 041851.1 + 281433 64.7132 28.2425 7.96 125.66 8.61 −24.65 26.11 164513538249595136 041847.0 + 282007 64.6960 28.3353 7.95 125.77 8.30 −25.31 26.63 164422961683000320 041941.2 + 274948 64.9220 27.8299 7.91 126.37 9.94 −24.96 26.87 152118881108855680 042445.0 + 270144 66.1878 27.0290 7.89 126.73 8.39 −26.84 28.13 146767764173923328 043858.5 + 233635 69.7442 23.6097 7.89 126.82 8.64 −21.20 22.89 163165738856771200 041514.7 + 280009 63.8114 28.0025 7.88 126.88 8.55 −25.52 26.92 146881048231272192 043933.6 + 235921 69.8902 23.9891 7.87 127.12 7.28 −20.99 22.22 152511475478780416 042155.6 + 275506 65.4819 27.9183 7.85 127.37 10.75 −27.22 29.27 151793082068521856 043114.4 + 271017 67.8102 27.1715 7.84 127.49 9.17 −27.58 29.06 164445437248152832 042026.0 + 280408 65.1087 28.0691 7.84 127.51 8.33 −26.07 27.37 146764809236423808 043901.6 + 233602 69.7568 23.6007 7.82 127.81 8.57 −21.85 23.47 162758236656524416 041447.8 + 264811 63.6995 26.8030 7.82 127.93 9.02 −22.45 24.20 148037764527442944 043619.0 + 254258 69.0796 25.7163 7.81 128.02 8.91 −27.47 28.88 163184366130809984 041412.9 + 281212 63.5539 28.2033 7.80 128.13 8.93 −29.05 30.40 147606657186323712 043527.3 + 241458 68.8641 24.2496 7.80 128.22 6.05 −20.77 21.64 151327159721125888 042945.6 + 263046 67.4403 26.5128 7.80 128.23 6.87 −20.97 22.06 147801339463632000 043301.9 + 242100 68.2582 24.3499 7.80 128.24 6.37 −20.47 21.44 162757545164429696 041447.3 + 264626 63.6971 26.7739 7.78 128.47 9.48 −22.69 24.59 163246832135164544 041314.1 + 281910 63.3090 28.3195 7.76 128.85 8.37 −24.40 25.80 164698634160139264 041733.7 + 282046 64.3906 28.3462 7.76 128.88 9.18 −25.55 27.15

Table 3 continued on next page 16 Table 3 (continued)

Gaia DR2 ID SSTtau ID R.A. Dec. Parallax Distance PMRA PMDec µ

[deg] [deg] [mas] [pc] [mas yr−1] [mas yr−1] [mas yr−1]

164702070133970944 041749.6 + 282936 64.4569 28.4933 7.75 129.03 6.90 −24.62 25.57 151373820245230080 042920.7 + 263340 67.3363 26.5611 7.74 129.24 7.91 −20.41 21.89 149369139966814976 042936.0 + 243555 67.4003 24.5987 7.73 129.42 8.57 −20.20 21.94 164666022471759232 041628.1 + 280735 64.1171 28.1265 7.70 129.84 6.85 −25.90 26.80 164409359522965120 041830.3 + 274320 64.6263 27.7223 7.70 129.89 8.73 −26.27 27.68 145238687096970496 043508.5 + 231139 68.7855 23.1943 7.69 129.96 7.24 −20.98 22.19 147796013704188928 043231.7 + 242002 68.1324 24.3341 7.69 130.03 7.12 −21.50 22.65 147796013704189440 043230.5 + 241957 68.1274 24.3325 7.68 130.21 6.65 −21.86 22.85 146277553787186048 043223.2 + 240301 68.0972 24.0503 7.68 130.24 7.36 −22.43 23.60 164705368668853120 041738.9 + 283300 64.4123 28.5500 7.68 130.27 6.87 −25.25 26.17 164536250037820160 042158.8 + 281806 65.4952 28.3017 7.67 130.33 9.01 −26.39 27.88 151028990206478080 043203.2 + 252807 68.0138 25.4687 7.67 130.39 8.09 −22.81 24.20 146285112929523456 043023.6 + 235912 67.5986 23.9868 7.67 130.40 4.73 −21.97 22.48 164518589131083136 041831.1 + 282716 64.6297 28.4544 7.67 130.44 8.68 −25.10 26.56 147806733942555008 043215.4 + 242859 68.0643 24.4831 7.67 130.46 5.02 −21.38 21.96 147790202612482560 043334.0 + 242117 68.3919 24.3547 7.66 130.50 5.88 −20.55 21.38 152226491513195648 042457.0 + 271156 66.2379 27.1989 7.66 130.57 8.36 −26.75 28.02 147831571737487488 043310.0 + 243343 68.2918 24.5619 7.66 130.60 7.25 −21.23 22.43 163182888662060928 041411.8 + 281153 63.5496 28.1981 7.63 131.09 9.08 −23.89 25.56 146366442430208640 042959.5 + 243307 67.4980 24.5520 7.63 131.12 8.18 −21.44 22.95 148017561002336384 043342.9 + 252647 68.4289 25.4462 7.63 131.14 5.13 −22.77 23.35 164738521519622656 041414.5 + 282758 63.5609 28.4660 7.62 131.24 9.50 −23.57 25.41 151297958238753664 042951.5 + 260644 67.4648 26.1124 7.62 131.28 5.95 −21.01 21.84 150393571269837184 041810.7 + 251957 64.5450 25.3325 7.61 131.36 8.83 −23.34 24.95 164684340508950144 041539.1 + 281858 63.9132 28.3162 7.61 131.49 9.25 −24.38 26.08 164504467278644096 041926.2 + 282614 64.8595 28.4372 7.59 131.70 8.36 −25.47 26.81 163184366130809472 041413.5 + 281249 63.5566 28.2136 7.58 131.94 8.59 −24.42 25.88 163184091252903936 041417.0 + 281057 63.5709 28.1826 7.55 132.44 8.28 −24.16 25.54 152917298349085824 042515.5 + 282927 66.3147 28.4909 7.52 133.06 10.79 −25.05 27.27 152362491654557696 042039.1 + 271731 65.1633 27.2920 7.51 133.07 10.41 −26.09 28.09 147847072275324416 043150.5 + 242418 67.9607 24.4048 7.50 133.33 4.46 −22.96 23.39 151262876946558976 042657.3 + 260628 66.7388 26.1078 7.50 133.36 5.19 −20.71 21.35 151125919028356352 043336.7 + 260949 68.4033 26.1636 7.50 133.40 8.16 −17.37 19.19 163179521407696384 041505.1 + 280846 63.7715 28.1460 7.49 133.57 8.46 −24.48 25.90 152516079683687680 042306.0 + 280119 65.7754 28.0220 7.47 133.88 7.93 −26.68 27.84 148450085683504896 043835.2 + 261038 69.6471 26.1773 7.46 133.96 4.89 −21.78 22.32 147869784062378624 043051.3 + 244222 67.7141 24.7061 7.45 134.22 7.05 −20.94 22.10 151265002954775936 042727.9 + 261205 66.8667 26.2013 7.42 134.69 1.81 −23.45 23.52 164514053645658752 041901.9 + 282233 64.7583 28.3758 7.40 135.07 9.19 −25.76 27.35 151374198202645376 042942.4 + 263249 67.4270 26.5469 7.40 135.12 6.90 −21.21 22.30 162967384383246336 041557.9 + 274617 63.9917 27.7714 7.37 135.67 7.82 −24.65 25.86 163181342473839744 041417.6 + 28060 63.5734 28.1026 7.37 135.69 8.34 −23.32 24.76 148172179824515968 044148.2 + 253430 70.4511 25.5751 7.34 136.16 4.51 −19.61 20.12 148112913570653568 044221.0 + 252034 70.5876 25.3428 7.34 136.16 4.89 −19.42 20.03 163233981593016064 041327.2 + 281624 63.3635 28.2734 7.34 136.30 7.44 −23.84 24.97 148401565437820928 044008.0 + 260525 70.0334 26.0903 7.34 136.32 5.73 −20.13 20.93 148400229703257856 043944.8 + 260152 69.9370 26.0312 7.31 136.85 7.46 −22.11 23.33 153001307909276928 042916.2 + 285627 67.3176 28.9409 7.30 137.05 −6.78 5.99 9.05 147818450613367424 043455.4 + 242853 68.7309 24.4813 7.29 137.20 3.48 −20.99 21.27 164470794735041152 041618.8 + 275215 64.0786 27.8708 7.28 137.29 7.47 −24.93 26.02 164506116546058112 041749.5 + 281331 64.4565 28.2254 7.28 137.37 8.81 −25.22 26.71 164474986623118592 041612.1 + 275638 64.0505 27.9439 7.27 137.49 8.89 −25.72 27.21 152029992465874560 042420.9 + 263051 66.0871 26.5141 7.27 137.59 9.25 −27.37 28.89

Table 3 continued on next page 17 Table 3 (continued)

Gaia DR2 ID SSTtau ID R.A. Dec. Parallax Distance PMRA PMDec µ

[deg] [deg] [mas] [pc] [mas yr−1] [mas yr−1] [mas yr−1]

148449845165337600 043821.3 + 260913 69.5889 26.1537 7.23 138.31 5.47 −22.97 23.62 152518828462749440 042307.7 + 280557 65.7824 28.0992 7.19 139.05 9.65 −27.01 28.69 148449913884294528 043828.5 + 261049 69.6191 26.1803 7.17 139.38 6.13 −21.34 22.20 151262941369626752 042654.4 + 260651 66.7267 26.1141 7.15 139.91 3.98 −20.40 20.79 145157937416226176 043559.4 + 223829 68.9980 22.6413 7.13 140.33 11.85 −16.94 20.67 148384179410294272 044108.2 + 255607 70.2845 25.9353 7.10 140.83 7.20 −21.95 23.10 147441558642852736 044427.1 + 251216 71.1131 25.2045 7.09 141.01 6.45 −20.15 21.16 147679014500233728 044018.8 + 243234 70.0786 24.5427 7.07 141.50 −1.41 −43.35 43.38 163181308112262400 041426.2 + 280603 63.6095 28.1008 7.04 142.13 5.54 −27.64 28.19 151787064819255936 043126.6 + 270318 67.8613 27.0551 6.99 143.08 13.99 −19.89 24.32 148354733113981696 043903.9 + 254426 69.7665 25.7406 6.95 143.99 7.04 −20.61 21.77 148106316500918272 044303.0 + 252018 70.7628 25.3384 6.92 144.57 4.73 −20.21 20.75 163229544890946944 041353.2 + 281123 63.4721 28.1897 6.91 144.80 11.32 −22.68 25.35 148450875956969344 043814.8 + 261139 69.5620 26.1943 6.88 145.41 4.01 −23.17 23.51 148420639387738112 043800.8 + 255857 69.5036 25.9825 6.87 145.50 4.90 −22.63 23.16 152643240779301632 042900.6 + 275503 67.2529 27.9175 6.87 145.65 8.65 −25.26 26.70 145196527698016512 043319.0 + 224634 68.3295 22.7761 6.77 147.67 10.94 −20.15 22.93 145947077527182848 043309.4 + 224648 68.2895 22.7801 6.71 148.98 10.67 −16.76 19.87 148374391180009600 043955.7 + 254502 69.9823 25.7505 6.70 149.27 6.19 −20.34 21.26 150501362066641664 042216.4 + 254911 65.5686 25.8199 6.61 151.26 14.13 −19.65 24.20 148141775750936960 044039.7 + 251906 70.1658 25.3183 6.57 152.20 6.35 −20.57 21.53 151130591952773632 043307.8 + 261606 68.2826 26.2684 6.57 152.25 7.17 −17.31 18.74 151037064744973696 043158.4 + 254329 67.9936 25.7249 6.55 152.60 7.55 −21.14 22.45 145133786815830784 043541.8 + 223411 68.9244 22.5698 6.53 153.25 10.96 −17.96 21.04 147373010964871040 044642.6 + 245903 71.6776 24.9842 6.48 154.25 4.60 −19.52 20.06 152109054223716480 042423.2 + 265008 66.0968 26.8356 6.46 154.73 11.49 −18.35 21.65 145950895754320384 043224.1 + 225108 68.1007 22.8522 6.44 155.36 9.99 −17.43 20.09 152108882425024128 042426.4 + 264950 66.1103 26.8305 6.43 155.51 11.58 −17.86 21.29 151283870746458496 042629.3 + 262413 66.6225 26.4037 6.42 155.88 10.90 −17.85 20.92 145209442664192896 043552.8 + 225058 68.9703 22.8495 6.39 156.53 10.95 −16.53 19.83 148196510814073728 044110.7 + 255511 70.2950 25.9198 6.38 156.81 4.52 −20.11 20.61 163183644576299264 041449.2 + 281230 63.7054 28.2084 6.37 156.92 10.65 −21.17 23.70 145213192171160064 043553.4 + 225408 68.9730 22.9024 6.36 157.15 11.37 −18.48 21.70 152288824375681536 042216.7 + 265457 65.5699 26.9158 6.35 157.57 11.31 −17.60 20.92 152098299625634816 042247.8 + 264553 65.6996 26.7646 6.34 157.67 10.74 −17.14 20.23 145209618758377856 043547.3 + 225021 68.9473 22.8393 6.30 158.63 13.52 −15.90 20.87 145203159127518336 043352.0 + 225030 68.4668 22.8416 6.30 158.71 8.90 −17.07 19.25 144936836795636864 043917.7 + 222103 69.8242 22.3509 6.29 158.87 10.47 −17.38 20.29 145157941711889536 043558.9 + 223835 68.9956 22.6431 6.29 158.94 10.81 −15.77 19.12 145196252820109440 043326.2 + 224529 68.3593 22.7581 6.28 159.17 8.62 −16.75 18.84 145213295250374016 043552.0 + 225503 68.9671 22.9177 6.28 159.22 8.78 −8.09 11.94 148010281032823552 043339.0 + 252038 68.4129 25.3438 6.28 159.34 9.33 −18.29 20.53 152000786688289664 042444.5 + 261014 66.1858 26.1705 6.27 159.57 11.87 −17.32 21.00 148289831863907840 044138.8 + 255626 70.4118 25.9407 6.26 159.78 2.50 −15.48 15.68 164800235906366976 041542.7 + 290959 63.9283 29.1665 6.25 159.95 12.34 −17.75 21.62 164783811951433856 041639.1 + 285849 64.1631 28.9803 6.25 160.04 4.97 −15.00 15.80 148116276529733120 044207.7 + 252311 70.5325 25.3866 6.25 160.12 −0.74 −14.15 14.17 146319193494413696 042745.3 + 235724 66.9392 23.9567 6.24 160.18 11.27 −16.57 20.04 152293149405058816 042146.3 + 265929 65.4430 26.9914 6.23 160.47 11.92 −18.33 21.86 152104381299305600 042449.0 + 264310 66.2044 26.7195 6.21 160.97 10.61 −17.05 20.08 145132927822383616 043520.2 + 223214 68.8343 22.5373 6.20 161.40 9.83 −16.63 19.32 145203811962545152 043410.9 + 225144 68.5459 22.8623 6.18 161.77 8.90 −17.27 19.43 145213875069914496 043520.8 + 225424 68.8371 22.9066 6.18 161.83 9.72 −19.25 21.56

Table 3 continued on next page 18 Table 3 (continued)

Gaia DR2 ID SSTtau ID R.A. Dec. Parallax Distance PMRA PMDec µ

[deg] [deg] [mas] [pc] [mas yr−1] [mas yr−1] [mas yr−1]

145212711134828672 043542.0 + 225222 68.9252 22.8729 6.17 162.07 10.02 −16.77 19.54 145210099794710272 043551.0 + 225240 68.9629 22.8777 6.16 162.32 6.32 −28.15 28.85 145225596036660224 043456.9 + 225835 68.7373 22.9765 6.15 162.68 11.70 −16.41 20.16 147562470562750720 043649.1 + 241258 69.2049 24.2163 6.14 162.85 43.42 −13.26 45.40 152099055539792000 042224.0 + 264625 65.6002 26.7738 6.13 163.27 11.41 −17.86 21.19 147248216395196672 044518.2 + 242436 71.3258 24.4101 6.11 163.54 −15.85 −2.85 16.10 145951789107603200 043249.1 + 225302 68.2047 22.8841 6.08 164.53 7.43 −15.79 17.45 145213192171159552 043554.1 + 225413 68.9757 22.9037 6.03 165.95 11.87 −9.99 15.51 152305248330621184 042134.5 + 270138 65.3942 27.0273 5.99 167.00 11.77 −16.63 20.38 164800815725933312 041524.0 + 291043 63.8505 29.1787 5.97 167.54 10.74 −19.44 22.20 152349022637314176 042025.5 + 270035 65.1065 27.0098 5.87 170.35 11.35 −17.73 21.05 145220064117853696 043610.3 + 225956 69.0433 22.9988 5.84 171.24 10.81 −15.96 19.27 146050057959093632 043119.0 + 233504 67.8295 23.5846 5.83 171.56 8.08 −16.60 18.47 145203704587705088 043415.2 + 225030 68.5637 22.8418 5.82 171.97 10.08 −17.50 20.19 151129011404806912 043344.6 + 261500 68.4361 26.2500 5.77 173.26 6.51 −17.31 18.50 145213187879627776 043552.7 + 225423 68.9700 22.9064 5.64 177.15 8.82 −13.95 16.51 145217379763796992 043638.9 + 225811 69.1622 22.9699 5.44 183.91 9.55 −15.97 18.61 152361426502650496 042115.2 + 272101 65.3136 27.3502 5.41 184.86 2.96 −4.53 5.41